Engineering geophysical investigation around ungwan doka, shika area within the basement complex of north western nigeria.

Journal of Environment and Earth Science www.iiste.org
ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online)
Vol 2, No.7, 2012

Engineering Geophysical Investigation Around Ungwan Doka,
Shika Area within the Basement Complex of North-Western
Nigeria
⃰ FADELE S.I (M.Sc), JATAU B.S (Ph.D) AND UMBUGADU A. (M.Sc)
Nasarawa State University, Keffi, Nigeria
⃰ Email: fadeleidowu@yahoo.com +2348066035524; bsjatau@yahoo.co.uk +2348034529326

Abstract
Geophysical investigation for engineering or environmental studies was carried out around Ungwan Doka of
Shika area which falls within the Basement Complex of North-Western Nigeria. The study is aimed at evaluating
the competence of the near surface formation as foundation materials, and to unravel the subsurface profile
which in turn determines if there would be any subsurface lithological variation(s) that might lead to structural
failure at the site and evaluating the groundwater potential of the site and determining the level of safety of the
hydrogeologic system. Vertical Electrical Sounding (VES), using Schlumberger configuration was adopted. A
total of 18 VES was conducted. The data obtained were subjected to 1-D inversion algorithm to determine the
layer parameters. The geoelectric section revealed two to four lithologic units defined by the topsoil, which
comprises clayey-sandy and sandy lateritic hard pan; the weathered basement; partly weathered/fractured
basement and the fresh basement. The resistivity values range from 26 m - 373 m; 77 m - 391 m; 473 m -
708 m; and 1161 m - 3600 m in the topsoil, weathered, fractured basement and fresh basement respectively.
Layer thicknesses vary from 0.38m – 6.58m in the topsoil, 1.1m – 33.04m in the weathered layer, 5.86m – 34.1m
in the fractured basement. Depth from the surface to bedrock/fresh basement generally varied between 2.65m
and 37.75m. Based on the resistivity values, it is concluded that the subsurface material up to the depth of 25m is
competent and has high load-bearing capacity. However, resistivity values less than 100 m at depths of
10m-15m indicate high porosity, high clayey sand content and high degree of saturation which are indications of
soil conditions requiring serious consideration in the design of massive engineering structures. The
hydrogeologic system at the site is vulnerable to contamination. Hence, the result reasonably provide a basis for
which groundwater potential zones are appraised for safety in case potential sources of groundwater
contamination sites such as septic tanks and sewage channels are planned for the area under study.
Key words: VES, Top soil, Weathered Basement, Partly weathered or Fractured Basement, Fresh ,Basement

1. Introduction
The failure statistic of structures such as buildings, tarred roads and bridges throughout the nation is increasing
geometrically. Most of these failures were caused by swelling clays (Blyth and Freitas, 1988). In recent times,
the collapse of civil engineering structures has been on the increase for reasons associated with subsurface
geological sequence (Omoyoloye et al., 2008). The foundation of any structure is meant to transfer the load of
the structure to the ground without causing the ground to respond to uneven and excessive movement. In order to
achieve this, most buildings are supported on pads, strips and rafts or piles (Blyth and Freitas, 1988). Therefore
the knowledge of the probable cause of rampant failure of building foundations due to subsurface movements
giving rise to cracks or structural differential settlements has been a great concern to geoscientists. This has
helped to distinguish between a continuing movement, which is often more likely to be a problem and those of
single events, which may not require repair depending on the extent of damage. However, adequate insight on
the types and patterns of foundation-based cracks and their evaluation has necessitated the need to consider the
geological and geophysical basis for buildings’ failure and adequate precaution taken to minimize such disaster.
The amount, type and direction of foundation movement are commonly noted from the bulging of brick or
masonry blocks. These in turn reveal the risk of vertical collapse or horizontal dislocation. The risk could be
traced to the height of construction, materials used for the building, site factor, earth loading or water. Other
factors include the seismic action, atmospheric disaster and accident (Omoyoloye et al., 2008). If cracks are old
with no sign of continuing or recurrent movement, building inspectors accept monitoring rather than quickly
recommending repairs. Most house settling cracks are basically caused by either the differences in expansion and
compression coefficients of the construction materials, relative changes in the shapes and sizes of saturated soils
or the dynamic earth. The need for subsurface geophysical investigation has therefore become very imperative so
as to prevent loss of valuable properties and lives that always accompany such a failure. Foundation evaluation
of a new site is necessary so as to provide subsurface and aerial information that normally assist civil engineers,
builders and town planners in the design and siting of foundations of civil engineering structures (Omoyoloye, et
al., 2008). Geophysical methods such as the Electrical Resistivity (ER), Seismic refraction, Electromagnetic

17

Vol 2, No.7, 2012

(EM), Magnetic and Ground Penetrating Radar (GPR) are used singly or in combinations for engineering site
investigations. The applications of such geophysical investigation are used for the determination of depth to
bedrock, structural mapping and evaluation of subsoil competence (Burland and Burbidge, 1981; Burger, 1992).
The engineering geophysical investigation was carried out at Ungwan Doka in Shika area, Kaduna State,
North-Western Nigeria, aimed at determining the depth to the competent stratum in the subsurface, delineation
of areas that are prone to subsidence or some form of instability, evaluating the groundwater potential of the site
and determining the level of safety of the hydrogeologic system in the study area.

2. Location and Topography of the Study area
The study area lies between Latitudes 110 10’ 49”N - 110 11’ 05” N and Longitudes 70 35’40”E - 70 38’ 50” E.
The site is situated along the Sokoto road, North West of Zaria (Fig. 1). The topography is that of high plain (flat
terrain) of Hausa land. The site is located within the tropical climatic belt with Sudan Savannah vegetation. The
environment is Savannah type with distinct wet and dry season. The rainfall regime is simple but with slight
variation which consists of wet season lasting from May to September and characterized by heavy down pour at
the start and end of the rainy season. The annual rainfall varies between 800 mm to 1090 mm while the mean
annual temperature ranges between 240C to 310C reaching a maximum of about 360C around April (Hore,1970;
Goh and Adeleke, 1978).

3. Geology of Study Area
The study area is laid on undifferentiated Basement Complex. Though there were no rock out-crops within the
site, observation however revealed that the weathered bedrock in some existing hand-dug wells within the site
and environs indicates the occurrence of granitic rocks within the site which are porphiritic in texture. The study
area falls within the Metasediments of the Basement Complex (McCurry, 1970). The Basement Complex in
Kaduna state was affected by an Orogeny, which predated the emplacement of the Older Granite. During this
event, deformation of the basement produced north-south trending basins of Metasediment in the form of
Synclinoria. Tertiary earth movements tilted the Metasediments to north and warped the basement along the axis
of the uplift pass through the present Kaduna state having northwest trend. They have a pronounced effect on the
drainage pattern of the state. Through the process of metamorphism, migmatization and granitization that
occurred within at least two tectono-metamorpic cycles, the rocks were largely transformed into migmatites and
granite gneiss, with some relics of the original gneisses McCurry (1976). The Basement Complex was later
intruded by series of intermediate and acid plutonic rocks during the Pan African Orogeny according to McCurry
(1976). Oyawoye (1970), showed that there is structural similarity between the study area and the rest of West
Africa. (MacLeod et al 1971), reported that newer basalts often overlie alluvial deposits. The Younger Granites
are high level discordant intrusions in the Basement Complex and occupy approximately 8% of the total surface
area of Nigeria according to Rahaman (1976).

4. Methodology
Vertical Electrical Soundings (VES) using Schlumberger array were carried out at eighteen (18) stations. A
regular direction of N-S azimuth was maintained in the orientation of the profiles. Overburden in the basement
area is not as thick as to warrant large current electrode spacing for deeper penetration (Oseji, et al., 2005;
Okolie, et al., 2005), therefore the largest Current electrode spacing AB used was 200m, that is, 1/2AB=100m.
The principal instrument used for this survey is the ABEM (Signal Averaging System, (SAS 300) Terrameter.
The resistance readings at every VES point were automatically displayed on the digital readout screen and then
written down on paper.

5. Results and Discussion
Shlumberger array shown in figure 2 was adopted for the survey. A and B are point current electrodes through
which current is driven into the ground, while M and N are two potential electrodes to record the potential
distribution in the subsurface within the two current electrodes.
From Ohm’s law, the current I and potential V in a metal conductor at constant temperature are related as
follows:
V = IR (1)

Where R is the constant of proportionality termed resistance and it is measured in ohms. The resistance R, of a
conductor is related to its length L and cross sectional area A by;

R = ρL / A (2)

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Vol 2, No.7, 2012

Where ρ is the resistivity and it is a property of the material considered.
From equation (1) and (2),
V = IρL / A (3)

The vertical electrical sounding (VES) with Schlumberger array involves fixing the potential electrodes at point
M and N, and symmetrically increasing the current electrode separation AB about the centre by displacing A and
B outwardly in steps. This will increase the depth of penetration within the separation AB. Thus the varying
resistivity measured when electrode array position is varied in an inhomogeneous medium is termed apparent
resistivity.
For simple treatment, a semi-infinite solid with uniform resistivity, ρ, is considered. A potential gradient is
measured at M and N when current electrodes located on the surface of the equipotential surface is semi-spheral
downward into the ground at each electrode. The surface area will then be 2πL2, where L is the radius of the
sphere. Thus

V = Iρ / 2πL (4)

By deduction then, the potential at M (VM), due to the two current electrodes, is

VM = Iρ/{2π (1/r1 – 1/r2)} (5)

Similarly, the potential at electrode N (VN) is given by

VN = Iρ/{2π (1/r3 – 1/r4)} (6)

where r1, r2, r3 and r4 are shown in Figure 2.

The potential difference, ∆V, acrss electrodes M and N is VM – VN. If the body is inhomogeneous like the study
area, apparent resistivity (ρa) is considered,

ρa = K (∆V/ I) (7)

Where ρa is apparent resistivity in ohm-metre, and

K = 2π [(1/r1 – 1/r2) - (1/r3 – 1/r4)] -1 (8)

K is called the geometric factor whose value depends on the type of electrode array used.
For Schlumberger array, if MN =2b and 1/2AB = L then,

K = π (L2/2b – b/2) (9)
The geometric factor, K, was first calculated for all the electrode spacings using the equation 9; K= π (L2/2b –
b/2), for Schlumberger array with MN=2b and 1/2AB=L. The values obtained, were then multiplied with the
resistance values to obtain the apparent resistivity, ρa, values (equation 7). Then the apparent resistivity, ρa,
values were plotted against the electrode spacings (1/2AB) on a log-log scale to obtain the VES sounding curves
using an appropriate computer software IPI2win in the present study. Some sounding curves and their models are
shown in Fig.3. Similarly, geoelectric sections are shown in Figs. 4 and 5.Three resistivity sounding curve types
were obtained from the studied area and these are the H (ρ1>ρ2<ρ3), A (ρ1< ρ2<ρ3) and KH (ρ1>ρ2< ρ3>ρ4) type
curves. However, there are few points which show two geologic layer cases. The results of the interpreted VES
curves are shown in Tables 1 and 2. The modeling of the VES measurements carried out at eighteen (18) stations
has been used to derive the geoelectric sections for the various profiles (Figure 4 and 5). These have revealed
that there are mostly four and three geologic layers beneath each VES station, and two layer cases at three
different VES points. The geologic sequence beneath the study area is composed of top soil, weathered
basement, partly weathered/fractured basement, and fresh basement. The topsoil is composed of clayey-sandy
and sandy-lateritic hard crust with resistivity values ranging from 26 m to 391 m and thickness varying from
0.38m to 6.58m, thinnest at VES 12 and thickest at VES 13. It is however, observed from the geoelectric
sections that VES 10, 11, 12 and 13 are characterized with low resistivity values varying between 26 m to
99 m suggesting the clayey nature of the topsoil in these areas and possibly high moisture content. The second
layer is the weathered basement with resistivity values varying from 77 m to 391 m and thickness ranges
between 1.1m to 33.04m, thinnest at VES 16 and thickest at VES 6. The third layer is the partly weathered and
fractured basement with resistivity and thickness values varying between 473 m to 708 m and 5.86m to 34.1m

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Vol 2, No.7, 2012

respectively. The layer is extensive and thickest at VES 18 and thinnest at VES 16. The fourth layer is
presumably fresh basement whose resistivity values vary from 1161 m to 3600 m with an infinite depth.
Though the thickness of the bedrock is assumed to be infinite, the depth from the earth’s surface to the bedrock
surface varies between 2.65m to 37.75m. Quite a few of the profiles dipping and a negligible number of them
show synclinal and fractured structure. These formations have some geological, physical and near-surface
engineering significance.

6.1 Profile A-A’
Profile A-A’ geoelectric section suggests that the site is characterized by lateritic hard pan at different
consolidation levels within shallow depths, while gneiss and granites mainly, characterize the basements (Fig.4).
The fresh basements have synclinal structure which cut across the profile. The weathered/fractured basement has
a dipping layering. The probable feature that may cause building failure could be geologic feature like dipping
bedrock or synclinal structure. This is because while overburden materials fill the synclinal structure, their
columns undergo ground movement by subsidence and thereby could amount to uneven settlement at the
foundation depths of buildings. In other words, uneven stress distribution may occur at the foundation depths of
subsurface, that is one side of building structure may have a stronger support than the other adjacent of it.
Another factor that could contribute to structural defect of building is the seasonal variation in the saturation of
clay which causes ground movement and is caused by clay swells and shrinkages which are occasioned by
alternate wet and dry seasons. The area is characterized by clay soils with lateritic patches at shallow depths with
their thickness ranging between 1.06m and 4.14m.
6.2 Profile B-B’
The geoelectric section revealed clayey sandy topsoil having some lateritic hard crust patches (Fig. 5). The
synclinal structure at VES point 11 is not well pronounced and may not pose any serious danger to building
foundation. However, there is a deep weathering beneath VES point 17 and 18. The presence of laterite beneath
the clayey topsoil which hardly extends beyond 2.5m reduces the danger posed by clay formation to large
buildings. This area forms a good site for the erection of high-rise civil engineering structures.
6.3 Competence Evaluation
There are no indications of any major linear structure such as fracture or faults that could aid building
subsidence. The geologic sequence beneath the area is composed of thin layer of topsoil, thick weathered layer,
partly weathered/fractured basement and fresh bedrock. The topsoil constitutes the layer within which small civil
engineering structures can be constructed. From the table of resistivity values Table 1, the topsoil is composed of
sandy clay, clayey sand and patches of lateritic hard pans. Engineering competence of the subsurface can be
qualitatively evaluated from the layer resistivity. The higher the layer resistivity value, the higher the
competence of a layer; hence from the point of view of the resistivity value therefore, laterite is the most
competent of the delineated topsoil, followed by clayey sand and sandy clay being the least competent. Based on
the resistivity values, depths of about 8-10m can support small to medium size structures while depth in excess
of 25m can support massive civil engineering structures in the study area.
6.4 Groundwater Potential
Even though experience has shown that there is no direct relationship between groundwater yield and borehole
depth in a basement complex environment, studies (Bala and Ike, 2001; Omosuyi et al., 2008; Ariyo and
Osinawo, 2007) revealed that areas with thick overburden cover in such basement complex terrain has high
potential for groundwater. According to Ariyo and Oguntade (2009), in a basement complex terrain, areas with
overburden thickness of 15m and above are good for groundwater development. The highest groundwater yield
is often obtained from a weathered/fractured aquifer, or simply a subsurface sequence that has a combination of
a significantly thick and sandy weathered layer and fractured aquifer. Where the bedrock is not fractured, a
borehole can be located at a point having a relatively high layer resistivity greater than 150 m but less than
600 m (Olorunfemi, 2009). From the foregoing two parameters – overburden thickness and resistivity values,
VES 1, 2, 3, 4, 5, 6, 7, 17 and 18 can be considered to be productive zones for groundwater development in the
study area. Since the area is generally shallow to the water aquifer and groundwater in this area is vulnerable to
pollution, the depth of sewage system should be <10m to the weathered basement (aquiferrous zone) in order to
avoid groundwater contamination. It is suggested that potential sources of contamination site like sewage
channels should be sited far away from viable aquifer units to ensure safety consumption of groundwater within
the area.

7. Conclusion
The VES results revealed heterogeneous nature of the subsurface geological sequence. Though the geoelectric
section showed complexity in the subsurface lithology, there is however, no indication of any major
fracture/fault that could aid subsidence. The geologic sequence beneath the study area is composed of topsoil,

20

Vol 2, No.7, 2012

weathered layer, partly weathered/fractured basement, and fresh basement. The topsoil is composed of
clayey-sandy and sandy-lateritic hard crust with resistivity values ranging from 26 m to 391 m and thickness
varying from 0.38m to 6.58m, thinnest at VES 12 and thickest at VES 13. It is however, observed from the
geoelectric sections that VES 10, 11, 12 and 13 are characterized with low resistivity values varying between
26 m to 99 m suggesting the clayey nature of the topsoil in these areas and possibly high moisture content.
The second layer is the weathered basement with resistivity values varying from 77 m to 391 m and thickness
ranges between 1.1m to 33.04m, thinnest at VES 16 and thickest at VES 6. The third layer is the partly
weathered and fractured basement with resistivity and thickness values varying between 473 m to 708 m and
5.86m to 34.1m respectively. The layer is extensive and thickest at VES 18 and thinnest at VES 16. The fourth
layer is presumably fresh basement whose resistivity values vary from 1161 m to 3600 m with an infinite
depth. Though the thickness of the bedrock is assumed to be infinite, the depth from the earth’s surface to the
bedrock surface varies between 2.65m to 37.75m. A-curve type which shows a continuous and uniform increase
in resistivity predominates. This curve typifies an area showing characteristics of high load-bearing strength.
This is followed by HK-curve showing that some areas have overburden saturation which recharges the main
aquifer units. The rest of the curves are minority in number with H-type curve which has a minimum resistivity
intermediate layer underlain and overlain by more resistant materials reminiscent of areas promising for
groundwater development and also few 2-layer cases close to the bedrock are observed. Based on the resistivity
values of the different geoelectric layers, the various geologic units up to depth of 25m are competent and can
support massive civil engineering structures. The presence of laterite beneath the clayey topsoil which hardly
extends beyond 2.5m reduces the danger posed by clay formation to large buildings. Other probable causes of
foundation defects are the growth of tree roots, organic deposits, sink holes, cavities or ground surface saturation
due to seepages and this should be taken care of during building project implementation to ensure that buildings
erected at the site stands the test of time. In a basement complex terrain, areas with overburden thickness of
15m and above are good for groundwater development. The highest groundwater yield is often obtained from a
weathered/fractured aquifer, or simply a subsurface sequence that has a combination of a significantly thick and
sandy weathered layer and fractured aquifer. Where the bedrock is not fractured, a borehole can be located at a
point having a relatively high layer resistivity greater than 150 m but less than 600 m (Olorunfemi, 2009).
From the foregoing two parameters – overburden thickness and resistivity values, VES 1, 2, 3, 4, 5, 6, 7, 17 and
18 can be considered to be productive zones for groundwater development in the study area. To ensure safety
appraisal of groundwater consumption in the area, potential sources of contamination site should be sited far
away from viable aquifer units to ensure safety consumption of groundwater within the study area.

Acknowledgement
The field guide and contributions of Dr. B.S Jatau technically and financially cannot be over emphasized. His
supports, corrections and guides are gratefully acknowledged, you are indeed a good mentor. Words of wisdom
and encouragement from my fathers and mentors in geology matters, the likes of Prof. S. Abaa and Prof. N.G.
Obaje also make this paper work a huge success.

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Vol 2, No.7, 2012

References
Ariyo, S.O. and Oguntade, A.K. (2009). Geophysical Investigation for Groundwater Potential in
Mamu Area, Southwestern Nigeria. Medwell Online Journal of Earth Sciences, Vol.3, no.1, pp.10-13.
Ariyo, S.O. and Osinawo, O.O. (2007). Hydrogeophysical Evaluation of Groundwater Potentials of
Atan/Odosenbora. Medwell Online Journal of Earth Sciences, Vol.9, no.1, pp. 50-65.
Bala, A.E. and Ike, E.C. (2001). The Aquifer of the Crystalline Basement Complex Area of Africa. Quarterly
Journal of Engineering Geology, Vol.18, pp. 35-36.
Burger, R.H (1992), ‘Exploration Geophysics of the Shallow Subsurface’. Prentice Hall, U.S.A. pp. 30-56
Blyth, F.G.H and de Freitas, M.D., (1988). Geology for Engineers. Butler and Tannar Ltd, Frome and
London. Pp. 292-293.
Burland, J.B and Burbidge, M.C (1981). Settlement of Foundations on Sand and Gravel Proceedings of
the Institution of Civil Engineers, 78(1), pp. 1325- 1381.
Goh, C.L., and Adeleke, B.O., (1978). Certificate Physical and Human Geography’ Oxford University Press,
Ibadan,pp78-150.
Hore, P.N (1970). Weather and Climate of Zaria and its Region. (Ed.) By M.J. Mortimore, Department of
Geography, Occasional Paper No4. A.B.U. Zaria. pp. 41-54
McCurry, P. O. (1970). The Geology of Zaria sheet 102 S.W and its Region in Mortimore, M.J. (Ed).
Department of Geography occasional paper No.4, Ahmadu Bello University, Zaria. pp. 1-3.
McLeod W.N.; Turner D.C. and Wright, E.P. (1971). The Geology of Jos Plateau with 1:100,000 Sheets
147,148,168,169,189 and 190. Geol. Survey Nigeria Bulletin, 32.
Omosuyi, G.O., Ojo, J.S. and Enikanoselu, P.A. (2003). Geophysical Investigation for Groundwater around
Obanla-Obakekere in Akure Area within the Basement Complex of South-western Nigeria. Journal of
Mining and Geology, Vol.39, no.2, pp. 109-116.
Okolie, E.C., Osemeikhian, J.E.A., Oseji, J.O. and Atakpo, E. (2005). Geophysical Investigation of the Source of
River Ethiope in Ukwuani Local Government Area of Delta State. Nigerian Institute of Physics, Vol.17,
pp.30-45.
Olorunfemi M.O. (2009). Water resources, Groundwater Exploration, Borehole site selection, and Optimum
Drill Depth in Basement Complex Terrain: Journal of the Nigerian Association of Hydrogeologists.
Special Publication Series 1, pp. 1-20.
Omoyoloye, N.A., Oladapo, M.I. and Adeoye, O.O., (2008). Engineering Geophysical Study of Adagbakuja
Newtown Development, Southwestern Nigeria. Medwell Online Journal of Earth Science; Vol. 2(2);
pp. 55-63
Oseji, J.O., Atakpo, E. and Okolie, E.C. (2005). Geoelectric Investigation of the Aquifer Characteristics and
Groundwater Potential in Kwale, Delta State. Nigerian Journal of Applied Sciences and Environmental
Management, Vol.9, pp. 157-1600.

Oyawoye, M.O (1970). The Basement Complex of Nigeria. In: Dessauvagie, TFJ and White man, A.J (Eds)
African Geology. University Press, Ibadan Nigeria pp. 91-97.
Rahaman, M.A. (1976).Review of the Basement Geology of South western Nigeria. In: Kogbe (Ed.). Geology
of Nigeria, Elizabeth Publishing Company Lagos pp 41-58.

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Figure 1: Location Map Showing the Study Area (From Northern Nigerian Survey Map)
Study Area

23

Vol 2, No.7, 2012

Table 1: The results of the interpreted VES curves

24

Vol 2, No.7, 2012

r1 r2

Earth’s surface
A M N B
r3 r4

Figure 2: Four-general electrode configuration (Shlumberger Array).

25

Vol 2, No.7, 2012

26

Vol 2, No.7, 2012

VES VES 2 VES 4 VES VES VES VES 8 VES 9
1 VES 3 5 6 7
A A’
373 ࢹ࢓ 370 ࢹ࢓ 276 ࢹ࢓ 304 ࢹ࢓ 365 ࢹ࢓ 353 ࢹ࢓
257 ࢹ࢓ 272 ࢹ࢓
367 ࢹ࢓

૛૛૚ ࢹ࢓
59 ࢹ࢓ 708ߗ݉
298 ࢹ࢓
351 ࢹ࢓ 228 ࢹ࢓

77 ࢹ࢓

10
3115 ࢹ࢓
1765 ࢹ࢓

144 ࢹ࢓
391 ࢹ࢓
DEPTH (m)

473 ࢹ࢓

20
834 ࢹ࢓

522 ࢹ࢓

1362 ࢹ࢓

503 ࢹ࢓
30

1251 ࢹ࢓

1410 ࢹ࢓ 1450 ࢹ࢓

40

Lateritic hard pan (Top soil) Weathered layer

Partly weathered/fractured layer Fresh basement

27

Vol 2, No.7, 2012

Figure 4: Geoelectric section along profiles A-Ai

VES 10 VES 11 VES 12 VES 13 VES 14 VES 15 VES 16 VES 17 VES 18
B’
B 28 ࢹ࢓ 281 ࢹ࢓ 256 ࢹ࢓
26 ࢹ࢓
28 ࢹ࢓ 30 ࢹ࢓ 30 ࢹ࢓ 254 ࢹ࢓

316 ࢹ࢓ 347 ࢹ࢓ 358 ࢹ࢓
356 ࢹ࢓
261 ࢹ࢓
162 ࢹ࢓ 199 ࢹ࢓

519 ࢹ࢓
694 ࢹ࢓

302 ࢹ࢓ 3699 ࢹ࢓ 2593 ࢹ࢓
3307 ࢹ࢓

1270 ࢹ࢓
2935 ࢹ࢓
10

1519 ࢹ࢓ 658 ࢹ࢓

1410 ࢹ࢓
DEPTH (m)

20

30

1614 ࢹ࢓

40
3511 ࢹ࢓

Clay/clayey sandy (Top soil) Lateritic hard pan (Top soil)

Weathered layer Partly weathered/fractured layer

Fresh basement

Figure 5: Geoelectric section along profiles B-Bi

28

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